I'm assuming that this comes in the middle of your holiday and you'd be travelling across from Florida to the West coast. If that's correct, I'd be selling it to your client as a bonus - they only pay for transcon flights rather than transatlantic.
I'd charge the costs of the time certainly, plus all your expenses (and remember that First class as a YYUP (KKUP now) is classed as Economy ). I think I'd also add on the costs of some of the hotel at Disney, since you would be there enjoying the hotel if you were not in the conference.
Any consultant I use chares 100% of travelling time, so no worries with that as well, but be prepared to do some 'work' on the plane to compensate.

You want to hit them with an estimate of costs that will make them realise the sacrafice you're making for them, but not so much as to make them get very annoyed with you - it's all abot sharing the pain !